Longitudinal study of three views of mandibular third molar eruption in males

Effects of Angle class II correction with the Forsus fatigue resistant device on mandibular third molars : A retrospective study

PURPOSE

The goal was to evaluate the effects of Angle class II malocclusion treatment using the Forsus fatigue resistant device (FRD, 3M, St. Paul, MN, USA) on the position and angulation of mandibular third molars and retromolar space.

PATIENTS AND METHODS

In all, 58 class II patients (mean age 13.6 ± 1.8 years) treated with the FRD (FRD group) were compared with 51 class I patients (mean age 13.5 ± 1.6 years) who underwent orthodontic treatment (control group). A total of 109 mandibular third molars in the FRD group and 91 in the control group were evaluated. Changes in the retromolar space, angulation of the second (ɣ) and third molars (β), and the angle between these teeth (α) were assessed with panoramic radiographs taken at the beginning and the end of the treatment. Data were statistically analyzed.

RESULTS

At the end of the treatment, there were significant increases in ɣ and β in the FRD group and ɣ in the control group (p < 0.05). The decrease in α in the FRD group and increase in the control group were not significant (p > 0.05); however, this change led to a small significant change between the groups (p < 0.05). The retromolar space significantly increased in the FRD group compared to the control group (p < 0.05). No significant correlation was found between retromolar space and third molar uprighting in any of the groups (p > 0.05).

CONCLUSION

Class II correction with FRD led to mesialization of the lower arch which provided an increase in the retromolar space. Little improvement in the uprighting of the third molars occurred.

The Characteristics of Adjacent Anatomy of Mandibular Third Molar Germs: A CBCT Pilot Study in Patients with Osteogenesis Imperfecta

(1) Objectives: The aim of our study was to investigate the anatomical features of lower third molar and its adjacent anatomical connections in type I Osteogenesis Imperfecta (OI) patients through cone beam computed tomography (cbct). (2) Methods: The study was conducted among 25 patients, 13 patients with type I OI and 12 control patients (individuals with no disorders and no treatment); average age was 15.44 ± 2.06, 23 third molar germs for each group. The germs have been compared to the parameters using the Mann-Whitney test. A chi-square test was also used to investigate the correlation between the status case/control and tooth development stage. (3) Results: Mann-Whitney test showed significant differences between cases and controls: diameter of the tooth germ in toto (U = 93.5; p < 0.001), tooth development stage, (U = 145; p < 0.01), roots length (U = 44.5; p < 0.01), cementoenamel junction diameter (U = 157.5; p < 0.05), size of the pulp chamber (U = 95.5; p < 0.05). Type I OI is not associated with the relationship between the germ of mandibular third molar and alveolar canal on axial plane (χ² = 4.095; p = 0.129), and parasagittal (χ² = 4.800; p = 0.091). The association between type I OI and relationship with the germ of mandibular third molar and alveolar canal on the coronal plane has been significant (χ² = 9.778; p < 0.05) as the perforation of the lingual cortical bone in the region of mandibular third molar tooth germ (χ² = 11.189; p < 0.01). (4) Conclusions: The results confirm the cbct accuracy in the evaluation of bone density in type I OI patients giving also the opportunity to study the tridimensional anatomy of germs and the adjacent anatomical structures in order to avoid any perioperative complications.

Factors associated with spontaneous angular changes of impacted mandibular third molars as a result of second molar protraction

INTRODUCTION

This study aimed to identify significant factors affecting the spontaneous angular changes of impacted mandibular third molars as a result of second molar protraction. Temporary skeletal anchorage devices in the missing mandibular first molar (ML-6) or missing deciduous mandibular second molar (ML-E) with missing succedaneous premolar spaces provided traction.

METHODS

Forty-one mandibular third molars of 34 patients (10 male and 24 female; mean age 18.3 ± 3.7 years) that erupted after second molar protraction were included in this study. They were classified into upright (U) and tilted (T) groups. Linear and angular measurements were performed at the time of treatment initiation (T1) and of ML-6 or ML-E space closure (T2). Regression analyses were used to identify significant factors related to third molar uprighting.

RESULTS

Nolla stage (odds ratio [OR] 4.1), sex (OR 0.003 for male), third molar angulation at T1 (OR 1.1), missing tooth space (OR 0.006), rate of third molar eruption (OR 23.3), and rate of second molar protraction (OR 0.2) significantly affected third molar uprighting. Age, third molar angulation at T1, rate of third molar eruption, and rate of second molar protraction were significant factors for predicting third molar angulation at T2.

CONCLUSIONS

Available space for third molar eruption before and after second molar protraction is not associated with uprighting of erupting third molars. Older patients whose third molars are in greater Nolla stage, are in a more upright position at T1, and have a greater eruption rate have a greater chance for third molar uprighting. Alternatively, an increase in second molar protraction rate results in mesial tipping of the third molars.

The ability of orthodontists and oral/maxillofacial surgeons to predict eruption of lower third molar

Background

The aim of this study was to evaluate the ability of oral/maxillofacial surgeons (OMFSs) and orthodontists to predict third molar eruption by examining a simple panoramic radiograph in cases where full spontaneous eruption occurred.

Methods

Panoramic radiographs of 17 patients, 13–16 years of age, were obtained just after orthodontic treatment (T1), when the third molars were intraosseous. The radiographs at T1 were presented to 28 OMFSs and 28 orthodontists—who were asked to give a prognosis for the lower third molars on both sides (n = 34). The full spontaneous eruption of all third molars was clinically observed when patients were older than 18 years (T2). These teeth were clinically asymptomatic at T1 and T2.

Results

OMFSs decided by extractions in 49.6 % of cases while orthodontists in 37.8 % (p < 0.001), when the radiographs were examined at T1. Agreement between OMFSs and orthodontists was excellent (Kappa = 0.76, p < 0.0001), as well as intragroup agreement for both OMFSs (Kappa = 0.83) and orthodontists (Kappa = 0.96).

Conclusions

Despite a remarkable agreement for third molar prognosis, orthodontists and OMFSs were unable to predict lower third molar eruption by examining a simple panoramic radiograph. Both indicated extractions of a considerable number of spontaneously erupted asymptomatic teeth.

Timing of human mandibular third molar formation

BACKGROUND

Population differences in tooth formation using radiographs can be determined if the entire developmental sequence of a single tooth is studied. The only developing tooth visible radiographically from initiation to root completion is the third molar or wisdom tooth.

AIM

The timing of mandibular third molar formation was documented for two groups of children in England and two in South Africa.

SUBJECTS AND METHODS

Panoramic radiographs of White and Bangladeshi children from London and Black African and Cape Coloured children from South Africa were examined (age 5-24). Mean age of entering third molar stages (crypt appearance to root completion) was calculated using logistic regression and compared between sex and group using a t-test.

RESULTS

Average age of third molar stages was significantly (p < 0.001) later in three groups for almost all stages of the third molar compared to Black children. The average age of entering initial mineralization ranged from 7.97 to 9.74 years while average age of apex closed was 19.27-20.88.

CONCLUSION

These results show for the first time a significant difference in the timing of maturation of the mandibular third molar between groups with South African Black children being earlier than other groups.

Prediction of mandibular third-molar impaction in adolescent orthodontic patients

INTRODUCTION

The purpose of this study was to identify risk factors for mandibular third-molar impaction in adolescent orthodontic patients.

METHODS

Radiographs made before (T1) and after (T2) treatment and at least 10 years postretention (T3) of 134 patients that allowed accurate diagnosis of impaction vs eruption of at least 1 mandibular third molar were evaluated.

RESULTS

Univariate logistic regression analyses at T1 showed that the decision to extract premolars (P <.05), an increase of 1 mm in mesial molar movement (P <.05), and an increase of 1 mm in eruption space measured from second molar to Xi point (centroid of the ramus) (P <.01) reduced the risk of impaction by 63%, 22%, and 30%, respectively. An increase of 1 degrees in mandibular third-molar angulation relative to the occlusal plane increased the risk of impaction by 11% (P <.01). Multivariate logistic regression analyses at T1 showed that reduced eruption space (P <.01), signs of forward mandibular growth rotation (P <.01), and female sex (P <.05) increased the risk of impaction. However, association tests documented increased frequencies of extractions and more mesial molar movement in female patients with erupted third molars. Univariate logistic regression analyses at T2 showed that every millimeter of increase in eruption space measured from the second molar to the anterior border of the ramus and to Xi point reduced the risk of impaction by 29% and 22%, respectively (P <.01), whereas every degree of increase in the angle between the occlusal surface and the occlusal plane increased the risk of impaction by 11% (P <.01). Multivariate logistic regression analyses at T2 showed that increased eruption space reduced the risk of impaction (P <.05), whereas increased mesial angulation of the third-molar bud (P <.01) and signs of forward growth rotation (P <.05) increased the risk of impaction.

Possibilty of the lower third molar eruption: Radiographic analysis

Backgraund/Aim. To assess the possibility of the eruption of the lower third molar on the basis of the measured parameters: retromolar space, mesiodistal crown width of a molar and the third molar angulation. Methods. The investigation included 104 patients both sexes (43 boys, and 61 girls), 16 to 25 years old (meanage, 18 years). It was performed using the orthopanthomographic radiographs analysis of those patients. Each radiograph was covered by tracing paper, and the contoures of the followiny anatomic details were drawn: a) the crown and root contours of third molars, upper and lower central incisors, distal molars in occlusion, anterior edge of ramus mandible, b) lines: 1. the occlusal plane, 2. the line of retromolar space, 3. the mesiodistal crown width of third molar, 4. the axial shaft of the third molar and the distal angle between occlusal plane and the axial shaft of the third molar. The values were measured with an orthodontic caliper: the diameter of retromolar space, diameter of mesiodistal width, the value of distal angle between occlusal plane and axial shaft of molar. Results. A favourable angulation of the lower third molar (more than 60?) was found in, boys (left 27.90%, right 32.55%), girls (left 39.34%, right 37.77%). A favourable relationship between the diameters of mesiodistal width of the third molar and retromolar space was found in, boys, (left 13.59%, right 16.27%), girls, (left 8.19%, right 14.75%). A favorable relationship between the diameters of mesiodistal width of the third molar and the retromolar space and the angulation was found in boys, (left 9.30%, right 11.62%), girls, (left 6.56%, right 9.83%). Conclusion. There was not any statistically significant difference found between the relation of the retromolar value, third molar mesiodistal diameter, or of the third molar angulation to the left and the right side nor of their mutual relations in comparing boys and girls. A favorable prognosis was found in 9.33% of the patients.

Third molar angulation during and after treatment of adolescent orthodontic patients

The purpose of this study was to analyse the effect of premolar extraction therapy on third molar angulation during active treatment, and to test the significance of such changes on subsequent impaction of the third molars. Lateral cephalograms made before (T1) and after (T2) treatment and at long-term follow-up (T3) of 157 patients treated non-extraction (non-ex) or with extraction of four premolars (ex), all accurately diagnosed for impaction versus eruption of at least one third molar at T3, were evaluated. Linear regression models demonstrated that the maxillary third molars uprighted more from T1 to T2 (P < 0.05) and were less distally angulated at T2 (P < 0.01) in the ex than in the non-ex patients. No such differences were detected in the mandible (P > 0.05). The regression models also showed similar uprighting of the maxillary and mandibular third molars from T1 to T2 and similar angulation of the maxillary third molars at T2 in those patients with subsequent eruption and impaction (P > 0.05), but more mesially angulated mandibular third molars at T2 in the impaction patients (P < 0.01). Chi square testing demonstrated a higher frequency of distal tipping of the maxillary third molars from T1 to T2 in the impaction patients (P < 0.01), while mesial tipping from T1 to T2 of the mandibular third molars occurred with similar frequency in the two patient groups (P > 0.05). Chi square analysis also showed a higher frequency of greater than 30 degree distal angulation as well as an amount mesial angulation of the maxillary third molars at T2 (P < 0.01), and a higher frequency of greater than 40 degree mesial angulation of the mandibular third molars at T2 (P < 0.01) in patients with impaction than in those with eruption.

Third molar management: a case against routine removal in adolescent and young adult orthodontic patients

In the nearly two decades since the National Institutes of Health conference, controversy and uncertainty have continued with respect to the diagnosis and treatment of impacted, nondiseased third molars in adolescents and young adults. Articles published over the past 10 years have studied the issue from the vantage point of risk management. Those who favor prophylactic removal justify this action on three premises: 1. All impacted third molars are potentially pathologic; therefore, prophylactic removal reduces or eliminates risk of future disease. 2. The presence of third molars can cause late crowding. 3. Removal during adolescence and young adulthood reduces risks of operative and postoperative complications compared with older patients. Those who favor conservative management offer three counter arguments: 1. Although impacted third molars do pose a risk of a pathologic condition, the risk is relatively small in comparison with the risks of operative and postoperative complications and the costs of unnecessary removal. 2. Although some investigators have shown a statistical association of third molars and late anterior crowding, the association is not strong enough to allow prediction of patients at risk. This is due principally to the high degree of individual variability, suggesting that many other factors interact in the development of postadolescent crowding. 3. Although studies have shown that morbidity is reduced when impacted, nondiseased third molars are removed during adolescence or young adulthood, the cost-risk-benefit data do not justify routine removal. Proponents of prophylactic removal argue that the benefits outweigh the risks. Proponents of conservative management argue that the scientific evidence is inconclusive in support of prophylactic removal. Unfortunately, much of the clinical research has been flawed. This has led to contradictory interpretations that have not fully clarified the relative risks and benefits of early intervention. Untrustworthy data have served only to fuel the debate and controversy concerning proper protocols. However, careful analyses of the published research show that routine removal of impacted or unerupted, disease-free third molars cannot be justified. A case-by-case management protocol that requires monitoring development represents the consensus of most researchers in this field.

Root resorption of mandibular second molar teeth associated with the presence of the third molars

Although pressure resorption of second molars is associated with impacted and/or erupting third molars, the relationship between pressure resorption and age is unclear. In order to investigate this relationship, 3883 dental radiographs were studied in 3174 individuals of various ages. The incidence of superimposition of the second molar on the third molar was not elevated in any subgroup except that of women of 16-40 years of age. There were no age or sex differences for the incidence of second molar root resorption. In older individuals, root resorption associated with a completely impacted third molar was more frequent than with a partially impacted third molar, and root resorption at the apex was mainly seen in individuals over 50 years of age. There was a higher incidence of superimposition and root resorption in men than women. Apical root resorption may be seen long after the formation of completely impacted third molars in both genders.

A device to predict lower third molar eruption

This study was designed to create a transparent device to be superimposed on a panoramic tomogram taken of a patient at age 20 years to make predictions of future eruption or impaction of lower third molars. The device was developed from data on 40 lower third molars initially retained at age 20 years; one half of these remained impacted, and the other half of them erupted by age 26 years. Tracings were made from panoramic tomograms taken at age 20 years. The critical point for prediction in the overlay was the intersection of a horizontal reference line and the anterior border of the ascending ramus. To estimate this critical separation line, Bayes' Decision Theory was used. The sum of false negatives and false positives was least at a distance of 14.5 mm from the distal surface of the second molar. Mesial from this point, the probability of impaction was 76%; distal from this point, the probability of eruption was 72%. Tested against 35 initially unerupted lower third molars, the predictions made by the device and the actual clinical findings were in conformity in relation to 97% of the test teeth. It could thus be concluded that the method was simple to use and may prove a good addition for predicting lower third molar development.

Prediction of coronal size of third molars by factor and multiple regression analyses

Factor analysis and multiple regression analysis were made to establish a method for the prediction of the unerupted third molar size. The samples were dental casts of 138 adults (69 women and 69 men) who had all their teeth from the central incisor to the third molar, at least in one side of each maxillary and mandibular dentition. Mesiodistal and buccolingual tooth crown sizes were measured with sliding calipers. Five factors were selected from the factor analysis on the tooth crown sizes. Multiple regression analysis with the third molar as the dependent variable was carried out. Independent variables were selected on the basis of the factors obtained from the factor analysis. Two kinds of multiple regression equations were obtained (the first molar was used as an independent variable in one equation and the second molar was used in the other). The accuracy of the prediction was highest when the lateral incisor, the second premolar, and the second molar were used as independent variables in the maxillary dentition, and the central incisor, the first premolar, and the second molar in the mandibular dentition. The mean of the absolute values of the differences between the predicted values and the actual values was 0.5 mm in the maxillary third molar, and 0.42 mm in the mandibular third molar.

Accuracy of dimensional and angular measurements from panoramic and lateral oblique radiographs

OBJECTIVES

Dimensional and angular measurements from radiographs can be used in clinical dentistry to determine the inclination of impacted teeth, the relative position of roots and restorative abutments, and for implant site assessment. This study was carried out to assess the in-vitro accuracy of such measurements obtained from three rotational panoramic systems and two standardized lateral oblique projections (45 degrees and 60 degrees) using two cephalometric systems.

METHODS

Acrylic test models with wires positioned to represent the position and angulations of the teeth were used. Ten images were taken with Oralix Pan DC/1, Panelipse and Orthophos panoramic machines. Fourteen lateral oblique radiographs were also taken using two cephalometric units: an Orthophos and a Quint Sectograph. The models were repositioned between each exposure. Horizontal, vertical and angular dimensions of every tooth position on each radiograph were measured by three evaluators and compared using ANOVA at an a priori significance level of alpha = 0.05.

RESULTS

Assessment of vertical dimensions was consistently more accurate on lateral oblique projections than on the panoramic radiographs. In general, the most accurate horizontal measurements could also be made with the lateral oblique projections. No differences in angular measurement accuracy were found between any of the projections. The use of statistical means and standard deviations can be misleading in ranking accuracy where a consistent conversion factor can be applied.

CONCLUSIONS

While panoramic radiography is convenient for dimensional and angular assessments, lateral oblique radiographs taken with a standard cephalometric apparatus are an alternative when greater clinical accuracy is needed.

Predictive model for impaction of lower third molars

The study was carried out to create and test a model for predicting impaction of lower third molars on the basis of radiographic findings at age 20 years. Fifty-six initially unerupted lower third molars were followed up for 6 years. Five radiographic findings in panoramic tomograms at age 20 were taken as variables. Clinical status at age 26 was taken as response. The radiographic features studied were angulation of tooth, development of root, state of impaction, depth in bone, and relation of the tooth to the ramus of the mandible and the second molar. With the use of logistic regression, univariate and bivariate analyses, and clustering techniques, a decision tree was constructed that indicated accuracies of prediction on the basis of single variables or pairs of variables. The most important predictor was the type of impaction. The model predictions and test teeth findings were in agreement in 94% of instances. It was concluded that the model is suitable for predicting lower third molar impaction at age 20.

Changes in lower third molar position in the young adult

Changes in position of unerupted lower third molars between 18 and 21 years were examined in a group of 17 men and 24 women with intact lower arches. Mesiodistal third molar angulation, molar space, molar space condition, and buccolingual third molar angulation and the changes in these dimensions were measured on 60 degree cephalograms taken at 18 and 21 years. At 18 years molar space was inadequate by an average of 5.0 mm. Average changes in dimensions were statistically nonsignificant except for an increase in molar space of 0.7 mm. Changes in third molar position ranged from 39 degrees to -46 degrees in the mesiodistal and from 24 degrees to -24 degrees in the buccolingual dimension. Only 10 third molars did not change their mesiodistal angulation. Four third molars erupted fully during the observation period.

Risks and benefits of removal of impacted third molars. A critical review of the literature

A critical review of the literature about risks and benefits of the removal of impacted 3rd molar teeth is presented in 4 categories: risk of non-intervention, risk of intervention, benefit of non-intervention and benefit of intervention. There are well-defined criteria for removal of impacted 3rd molar teeth. Absolute indications and contra-indications for the removal of asymptomatic 3rd molar teeth cannot be established because no long-term studies exist which validate the benefit to the patient either of early removal or of deliberate retention of these teeth. The prudent course of action for the clinician to follow is based on rational clinical decision-making using traditional methods of evaluation to effect the optimal outcome, keeping the interests of the individual patient above all else.

Clinical follow-up study of third molar eruption from ages 20 to 26 years

The development of 412 upper and lower third molars was clinically followed up for 6 years in 120 students, starting at the age of 20 years. Clinical and radiographic examinations carried out at baseline and 6 years later showed that during the follow-up period almost half the third molars originally recorded as partially erupted had erupted. When the lower third molars were initially invisible, only 9% of them had erupted by age 26 years whereas 29% remained invisible. When third molars had been already erupted at baseline, only a few were extracted during the 6-year follow-up period. It was concluded that a certain proportion of third molars erupt relatively late, and therefore the need for surgical interventions may decrease with age during early adulthood.

Assessing the eruption of lower third molars on the basis of radiographic features

To determine radiographic features by which one could estimate whether lower third molars are likely to erupt after the age of 20 years, university students with a total of 84 unerupted or partially erupted lower third molars were followed up. Five radiographic features of each third molar were measured from the panoramic tomogram taken at age 20 years, and the status of third molars was examined for a second time at age 26 years. The results showed that the lower third molars that did erupt after the age of 20 years were initially: 1) root formation complete; 2) impacted in soft tissue; 3) vertical; 4) placed at the same occlusal level as the neighbouring second molar; 5) showed sufficient space between the ramus and the second molar. In contrast, the teeth that remained impacted at the age of 26 years showed such initial features as: 1) incomplete root formation; 2) embedding in bone; 3) mesioangularity; 4) situated at the cervical level of the neighbouring second molar. It was concluded that a panoramic tomogram taken at age 20 years revealed radiographic features on which an estimation of future eruption of mandibular third molars could be based.